It is known in the prior art to hermetically cap a MEMS device, and to make electrical connections between the MEMS device and a related integrated circuit via wire bonds outside of the hermetic cap.
It is also known to attach the related integrated circuit to the substrate of the MEMS device via a seal ring, such that the related integrated circuit acts as a cap to hermetically seal the MEMS device in a cavity. Such devices make the electrical connections between the MEMS device and the capping integrated circuit by providing electrically conductive interconnections extending directly between the substrate and related integrated circuit within the hermetic cavity.
However, it is known that typical backend films used for inter-metal isolation and top passivation in integrated circuits, such as PECVD oxide and PECVD nitride for example, can release (i.e., “outgas”) gasses into the cavity. Such gasses, once released into the inside of the device's hermetically sealed cavity, can cause much higher sealed pressure than desired, and adversely impact the performance of the MEMS device. For example, such gasses may cause an accelerometer or gyroscope to fail to meet their respective specifications. Even for devices that do not require a low pressure cavity environment within a cavity, this outgas can cause the pressure to be at or about 1 atmosphere, so the basic Q measurement for hermeticity screening may not be possible.